If you know or suspect who it is then you need to contact both the IRS and SSA and file a fraud case. I did not get my stimulus check and was constantly told its because someone used my SSN, then was told someone claimed me on their taxes. The only person that could have done that was my X-wife so I filed fraud cases and named her as a "suspect". I was then told constantly that my only option at this point was to claim it next year. I had settled in the fact that there was nothing else I could do and planned to wait until next year, or this year lol. And to my extreme surprise several months later (November to be exact) I got my stimulus check deposited into my account. SO my advice is to call both SSA and IRS and open the fraud cases against that person. Good luck.
